Extend CI to test operator storing on ghcr.io

GITHUB_TOKEN is auto_populated.

The MARIADB_OPERATOR_TOKEN is a secret provided by
the owner of https://github.com/mariadb-operator/mariadb-operator

that expires on Expires on Tue, May 27 2025.

.github/workflows/ci.yml

@@ -74,3 +74,15 @@ jobs:
         run: ${{ matrix.runs.mariadbtest }}
       - name: '"docker images"'
         run: ${{ matrix.runs.images }}
+      - name: login to repo
+        uses: docker/login-action@v2
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+      - name: push to repo
+        run: docker push ${{ matrix.name }} ghcr.io/MariaDB/mariadb:${{ matrix.name }}
+      - name: MariaDB Operator Test
+        run: gh workflow run test-image.yaml --repo mariadb-operator/mariadb-operator -f mariadb_image=ghcr.io/MariaDB/mariadb:${{ matrix.name }}
+        env:
+          GITHUB_TOKEN: "${{ secrets.MARIADB_OPERATOR_TOKEN }}"